1. Field of the Invention
This invention relates to the field of switching assemblies and, more particularly, to a momentary contact push button switch which has a tactile action and is adapted for use in keyboard assemblies.
2. Prior Art
There is a wide variety of devices having a keyboard assembly in which a plurality of depressable keys or push button switches are provided. One such device is the now popular "pocket calculator". The keyboard in such a device contains a plurality of switches each of which, when depressed, perform a separate operation. Because each switch may be depressed many times during the useful life of the calculator, the switch must be well constructed and not susceptible to excessive wear. Moreover, the large number of separate switches in a typical keyboard requires them to be made as simple and inexpensive as possible.
There are many types of push button switches which are designed to make electrical contact in various switch assemblies. For example, a conventional system is to provide a spring loaded key-switch combination in which the contact engagement has a "wiping" action. Such a system is shown by McMann et at, U.S. Pat. No. 3,544,987. While the switch of McMann does provide the desired electrical making and breaking of a circuit, such mechanisms are characterized by their expensive and complex construction, and because of the wiping action, tend to have excess wear and easy failure of the parts. For example, in the switches of McMann et al, as the button member is depressed, the sinusoidal-shaped spring is caused to extend or flex outward as the arms of the spring move into their desired position. When pressure is removed from the button, the spring once again moves back into its unflexed position. One can easily see that in such a system, the wiping action of the spring against the contact members causes the spring to wear out quickly. Moreover, there is no "feeling" associated with such a device which provides the user with an indication that the desired contact is being made.
Another type of push button switch for use in keyboard switching assemblies is disclosed by Walker, U.S. Pat. No. 3,849,611. In the invention of Walker, the switch includes a contact bar and spring contact leads cantilevered above and across the contact bar. When the button member is depressed, each of the spring leads is deformed downward and across the desired contact with a wiping action across the bottom of the button. This type of assembly also suffers from the shortcoming associated with the assembly of McMann in that there is still the same wiping action only in this case the wiping action is on the button member as opposed to the contact. And there is no "feel" in relation to making the desired contact. Moreover, the assembly of Walker requires that the spring members be coupled to the board and the button member installed separately. This is expensive and requires complex assembly steps. In most typical keyboard switch assemblies in which a plurality of keys are provided for independent operation in response to manual depression thereof, it is especially desirable to provide each push button or key with the requisite "feel" of making contact when the button is depressed. This enables the user to know that information has been inserted into the machine. Such a switch is referred to as having a "tactile" feel. Switches of this type, usually containing a spring, require an initial force to overcome the resistance of the spring, but then much less force to hold the spring down.
One prior art switch which discloses a means for obtaining the desirable tactile feel is Weidenman, U.S. Pat. No. 2,066,022. In the thumb switch of Weidenman, a uniquely designed spring which is shaped, in part, to a form of a "Witch of Agnes" is disposed at the end of a movable plunger member. When the plunger member is depressed the spring flexes inward but only after sufficient force is applied. It should be noted, however, that this type of switch would not be applicable in a keyboard assembly inasmuch as the spring is not designed to permit the plunger to contact any surface disposed thereunder. Moreover, there is no teaching in Weidenman of how to modify his switch such that it could be used in keyboard assemblies and the like.
The present invention is directed towards a unique push button switch designed to make a low current and low voltage connection from one conductor to another. By the use of the present invention a simple, yet effective solution to the aforementioned problems associated with prior art push button switches are overcome.